EP0323258B1 - Système de distribution de transmissions - Google Patents

Système de distribution de transmissions Download PDF

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Publication number
EP0323258B1
EP0323258B1 EP88312409A EP88312409A EP0323258B1 EP 0323258 B1 EP0323258 B1 EP 0323258B1 EP 88312409 A EP88312409 A EP 88312409A EP 88312409 A EP88312409 A EP 88312409A EP 0323258 B1 EP0323258 B1 EP 0323258B1
Authority
EP
European Patent Office
Prior art keywords
frequency
jamming signal
signal
jamming
receiver
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Expired - Lifetime
Application number
EP88312409A
Other languages
German (de)
English (en)
Other versions
EP0323258A2 (fr
EP0323258A3 (en
Inventor
David E. Wachob
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Arris Technology Inc
Original Assignee
Arris Technology Inc
General Instrument Corp
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Arris Technology Inc, General Instrument Corp filed Critical Arris Technology Inc
Publication of EP0323258A2 publication Critical patent/EP0323258A2/fr
Publication of EP0323258A3 publication Critical patent/EP0323258A3/en
Application granted granted Critical
Publication of EP0323258B1 publication Critical patent/EP0323258B1/fr
Anticipated expiration legal-status Critical
Expired - Lifetime legal-status Critical Current

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Classifications

    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04K—SECRET COMMUNICATION; JAMMING OF COMMUNICATION
    • H04K3/00—Jamming of communication; Counter-measures
    • H04K3/80—Jamming or countermeasure characterized by its function
    • H04K3/82—Jamming or countermeasure characterized by its function related to preventing surveillance, interception or detection
    • H04K3/825—Jamming or countermeasure characterized by its function related to preventing surveillance, interception or detection by jamming
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04K—SECRET COMMUNICATION; JAMMING OF COMMUNICATION
    • H04K3/00—Jamming of communication; Counter-measures
    • H04K3/20—Countermeasures against jamming
    • H04K3/28—Countermeasures against jamming with jamming and anti-jamming mechanisms both included in a same device or system, e.g. wherein anti-jamming includes prevention of undesired self-jamming resulting from jamming
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04K—SECRET COMMUNICATION; JAMMING OF COMMUNICATION
    • H04K3/00—Jamming of communication; Counter-measures
    • H04K3/40—Jamming having variable characteristics
    • H04K3/42—Jamming having variable characteristics characterized by the control of the jamming frequency or wavelength
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04N—PICTORIAL COMMUNICATION, e.g. TELEVISION
    • H04N7/00—Television systems
    • H04N7/16—Analogue secrecy systems; Analogue subscription systems
    • H04N7/166—Passage/non-passage of the television signal, e.g. jamming, band suppression
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04N—PICTORIAL COMMUNICATION, e.g. TELEVISION
    • H04N7/00—Television systems
    • H04N7/16—Analogue secrecy systems; Analogue subscription systems
    • H04N7/167—Systems rendering the television signal unintelligible and subsequently intelligible
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04K—SECRET COMMUNICATION; JAMMING OF COMMUNICATION
    • H04K2203/00—Jamming of communication; Countermeasures
    • H04K2203/10—Jamming or countermeasure used for a particular application
    • H04K2203/14—Jamming or countermeasure used for a particular application for the transfer of light or images, e.g. for video-surveillance, for television or from a computer screen

Definitions

  • This invention relates to electronic signal transmission and, more specifically, to a video or other communications signal distribution system which provides secure programming selectively available only to a restricted subset of system subscribers.
  • Video signal distribution applications e.g., CATV or MATV systems, often employ selected channels which may be received only by selected, authorized subscriber/recipients.
  • tiered CATV systems employ a base video service available to all recipients; and premium signals (such as movies, theatre and/or sporting events) available only to subscribers who pay for and are authorized to view the additional programming.
  • premium signals such as movies, theatre and/or sporting events
  • the extra subscriber authorization may be pre-arranged by subscription to extra program categories; or may be available on an impulse pay-per-view basis.
  • a mechanism must be employed to disable viewing of the additional programming by unauthorized viewers.
  • a number of such restrictive selective pay television systems have heretofore been employed. Included among such systems, a jamming signal has been employed within the frequency bounds of a video program to defeat tolerable reception for example as described in GB-A-1,041,405.
  • the jamming carrier prevents recovery of the synchronization signals required to reconstruct and display a television picture; and also per se represents video picture content interference.
  • the difficulty exists that on an organized or ad hoc basis, unauthorized subscribers may employ a narrow-band filter to remove the jamming signal, thus permitting reception.
  • jamming signals are included in both the transmitted audio and video signals such that at the receiver, the video signal can be unscrambled by comparison and cancelling out of the received jamming signal.
  • the frequency of the jamming signals may be varied, according to a schedule known to both broadcaster and subscriber.
  • GB-A-2079111 a fixed frequency jamming signal is heterodyned with a video signal at the transmitter and unscrambled by heterodyning at the receiver.
  • the present invention aims to provide an improved electronic signal distribution system.
  • a communication system comprising a transmitter and at least one authorised receiver and wherein, for the purpose of inhibiting unauthorised reception of transmitted communications, the transmitter comprises: means for generating a variable frequency jamming signal; means for including said variable frequency jamming signal in transmitted signals; and means for including in the transmitted signals information representative of the variable frequency of the jamming signal; and the receiver comprises: means responsive to said information received at the receiver for determining the frequency of the jamming signal; and means responsive to said determining means for removing said variable frequency jamming signal from said transmitted signals received at said receiver.
  • a transmitter and a receiver for use with such a system are also provided.
  • An exemplary embodiment of the invention comprises a specific, illustrative video distribution (CATV or MATV) system employing at least one channel characterized by a reception-defeating jamming signal which changes frequency periodically or, preferably, randomly.
  • the signal originating head end distributes information identifying the frequency of the jamming wave.
  • the jamming frequency specifying data is employed on a frequency agile basis to heterodyne the protected channel into a proper (fixed) frequency relationship with a notch band suppression filter to remove the jamming signal.
  • the secure channel with the jamming wave removed is then again shifted to its original or other intended frequency to permit normal reception either directly by a standard television receiver or via a frequency converter.
  • the instant apparatus provides for transmission and distribution of an array of video signals - as via a CATV or MATV cable (10 in Figs. 1 and 2).
  • a CATV or MATV cable (10 in Figs. 1 and 2).
  • a first subset of channels which are transmitted in the clear and which are distined for reception by all signal recipients connected to the distribution cable or the like.
  • Also included in the ensemble of signals is at least one video program which is protected, i.e., which is destined for reception only by those cable-connected subscribers who are authorized to receive the protected program.
  • a system employs one premium or protected channel haviang the standard approximate 6 megahertz spectrum m roughly centered ⁇ 3 mhz about frequency a mhz.
  • the head end transmits a jamming sinusoid within the frequency bounds a ⁇ 3 mhz of the protected channel.
  • the jamming signal would be transmitted at a fixed frequency giving rise to the possibility of purloined reception by a user who became equipped with a narrow band notch filter at the constant frequency of the jamming wave.
  • a jamming signal is employed - but not of fixed frequency. Rather, the frequency of the jamming wave changes from time to time - either through the whole band a ⁇ 3 mhz or, preferably, within limited frequency bounds j proximate the picture carrier shown in Fig. 3. This prevents defeat of the jamming signal by a fixed frequency notch or band reject filter since the jamming carrier on a statistical basis will repose within the frequency of such a fixed filter only a very small percentage of the time.
  • the apparatus of the present invention obviously must provide apparatus to create the variable frequency jamming carrier at the head end - and to eliminate this varying frequency signal at the receiver.
  • the head end apparatus varies the frequency of the jamming signal within the sub-frequency bounds j (or within the full frequency band m ) from time to time.
  • a predetermined frequency sequency may be employed, with predetermined timing. This would obviate the need for communicating un-jamming synchronizing information from the head end to the restoring subscriber equipment which may simply operate in accordance with the pre-specified frequency pattern which can be locally stored.
  • a random number generator(s) at the head end may act in concert with a microprocessor to cause a random jamming frequency to obtain within the prescribed frequency bounds for the jamming signal (with random timing).
  • the frequency assignment (and timing) is then transmitted by the head end to the signal restoring equipment - as by frequency shift keying (FSK) modulation on a system subcarrier, e.g., in the FM band; or in-band as via amplitude modulation on the audio subcarrier.
  • FSK frequency shift keying
  • the decrypting equipment at or nearby the subscriber locations receives the frequency and timing information from the subcarrier channel to permit decryption (jamming signal removal) in the manner described below.
  • a band reject filter blocks direct transmission to subscribers of the entire premium channel - and unintended upstream transmission of the decrypted clear signal.
  • a jamming signal eliminating path is employed which includes a narrow, notch band rejecting filter of fixed frequency.
  • the entire 6 mhz premium signal is then adjusted in frequency by frequency agile heterodyning apparatus such that the jamming frequency, wherever it then happens to be, will identically correspond in frequency to the frequency of the notch filter.
  • a second heterodyning process restores the entire premium program- with the jamming signal removed, to its original or other intended spectrum for direct recovery and display by either a standard television receiver, or by an intermediate frequency converter.
  • a frequency agile synthesizer is employed for the two heterodyning operations in the jamming signal eliminating path, under control of the jamming signal frequency information provided by the FSK modulation (or other frequency communications path) to maintain the frequency correspondence between the time varying frequency of the jamming wave and the fixed frequency of the band reject filter. Accordingly, reception by individual subscribers of the protected premium program is dictated by operative available jamming signal removing circuitry.
  • Jamming signals may be employed in a plurality of protected premium channels, where jamming occurs on a time division (i.e., time-interleaved) basis.
  • the premium program then transporting the jamming sinusoid is appropriately positioned with respect to the fixed frequency band rejecting filter such that all programs are delivered clear for reception.
  • a plurality of television signal sources 501, ..., 50 n supply differing television programs to a respective one of an array of modulators 521, ..., 52 n the outputs of which are linearly combined in a summing network or combiner 53.
  • one of the television signal sources 50 i with its following modulator 52 i , correspond to a video program for which access is to be restricted.
  • the post-modulation band for the protected program is centered about the frequency a . Since a television signal is approximately 6 megahertz wide, the band of the protected signal is substantially a-3 to a+3 megahertz.
  • a microprocessor 60 is employed at the head end and controls a frequency synthesizer 57.
  • the microporcessor 60 supplies a digital control word to the frequency synthesizer 57 which governs its output frequency in a manner per se well known for such devices.
  • the output of synthesizer 57 is a sinusoid of frequency j ′ within the band a ⁇ 3 mhz (or the lesser range j of Fig. 3) thereby jamming reception of the premium program.
  • the output frequency is also supplied to a frequency shift key modulator 62 which thus supplies a singal identifying the jamming frequency.
  • the microprocessor 60 changes its control word to synthesizer 57 and modulator 62 from time to time to alter the frequency of the jamming sinusoid - as in accordance with the output of a random number generator presumed internal to the microprocessor 60 but which may be implemented by a device external thereto.
  • the television programs at the output of modulators 521, ...,52 n , the jamming sinusoid from synthesizer 57, and the jamming frequency signalling band output of FSK modulator 62 are all supplied to the linear summing network 53 where they are combined.
  • the combined signals are applied via a cable driver 64 onto the distribution cable network 10.
  • Cable network 10 includes trunk, branch and other network constituents to disseminate the ensemble of head end signals to each of the system subscribers.
  • a system subscriber directly connected to distribution cable 10 can directly receive all clear channels. However, such a subscriber may not receive the protected signal in the i-th channel because the time varying jamming carrier will prevent reception.
  • decrypting apparatus shown in Fig. 2 is employed.
  • the Fig. 2 decryption structure may be employed within the subscriber's home as part of a converter or other terminal equipment. Preferably, however, such apparatus is located outside the subscriber's home under control of the system proprietor for enhanced security.
  • the head end distributed signal on cable 10 passes through a signal splitter 13 to a band reject filter 14 at least a ⁇ 3 mhz wide so that the entire premium signal spectrum m (Fig. 3) is blocked. All clear channels (i.e., all frequencies outside a ⁇ 3 mhz) pass through combiner/splitter 32 for delivery to the subscriber via the cable run 10a.
  • the incoming signal from the distribution cable 10 also passes through the lower branch of splitter 13 and through a splitter 17 to a receiver 20 which effects FSK demodulation.
  • the receiver 20 thus communicates the jamming frequency j ′ then in use at the head end to a microporcessor 21.
  • Microporcessor 21 appropriately controls a frequency synthesizer 25 to supply an output frequency y , the value of which will be described below.
  • the signal on cable 10 is also passed by splitters 13 and 17 to a band pass filter 18 which passes the a ⁇ 3 mhz premium signal of band m (Fig. 3) to a balanced mixer 26 which also receives frequency y from synthesizer 25.
  • the output of mixer 26 is supplied to a narrow band notch filter 30 which rejects frequencies at and very close to a value z megahertz.
  • the output of mixer 26 shifts the center frequency of the premium channel a to a value y - a .
  • the heterodyning process operates on a frequency agile basis changing the mixer input y to precisely that value z + j ′ which is required to eliminate the jamming carrier.
  • the above-described apparatus thus tracks and rejects the changing frequency jamming signal, creating a lower heterodyne band y-a-3 to y-a+3 mhz free of the jamming signal at the output of narrow notch filter 30.
  • a low pass filter 35 rejects all heterodyning products other than the difference band.
  • the selected lower or difference band centered around y-a mhz undergoes a second heterodyne process at a mixer 37 which may also use the frequency y .
  • the protected signal is restored to its original spectrum (a ⁇ 3 mhz) where it passes through splitter/combiners 44 and 32 in clear form suitable for reception by the subscriber connected to the cable run 10a.
  • Any offset may be algebraically added to y , if desired, to deliver the decrypted protected channel (without interference sinusoid) at a vacated spectrum allocation different from its position on the cable 10 is desired.
  • Figs. 1 and 2 The system of Figs. 1 and 2 has thus been shown to provide a frequency varying jamming signal which defeats unauthorized reception. Where reception is permitted, the Fig. 2 apparatus removes the jamming signal on a frequency agile basis to restore the protected channel to clear form suitable for reception.
  • a plurality of such channels can be implemented with one in-band interference carrier shared between channels on a time multiplexed basis, i.e, where the head end impresses a jamming signal within the band of one of the encrypted channels at a time.
  • the filters 14, 18 and 42 are made sufficiently wide to pass or block as appropriate the continguous array of protected channels; and the remainder of Fig. 2 will automatically operate in the manner above-discussed to automatically put the jamming signal (in whatever channel and at whatever frequency) at frequency z mhz for removal by filter 30 to provide all channels on a clear basis.
  • the foregoing discussion has assumed permanent authorization of the protected channel to subscribers connected to Fig. 2 equipment.
  • the Fig. 2 apparatus may alternatively be operated on an impulse, pay-per-view basis where the subscriber must signal a desire to receive a program.
  • This request signal for example in the form of a predetermined modulation on a sub-band signal, passes on cable run 10a through splitters 32 and 44 and through a low pass filter 45 to a detector 53.
  • detector 53 notes a service request, it appropriately signals microporcessor 21 as at a processor input or interrupt port.
  • the processor 21 responds by passing the received frequency information i' to synthesizer 25 to effect channel reception enablement in the manner above described.
  • Fig. 1 and Fig. 2 apparatus has thus been shcwn to flexibly and reliably provide one or more protected channels together with one or more clear channels for video signal distribution.

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  • Engineering & Computer Science (AREA)
  • Signal Processing (AREA)
  • Computer Networks & Wireless Communication (AREA)
  • Multimedia (AREA)
  • Radar, Positioning & Navigation (AREA)
  • Remote Sensing (AREA)
  • Two-Way Televisions, Distribution Of Moving Picture Or The Like (AREA)
  • Radio Transmission System (AREA)

Claims (13)

  1. Système de télécommunication comportant un émetteur et au moins un récepteur autorisé et dans lequel, dans le but d'empêcher une réception non autorisée de télécommunications émises, l'émetteur comporte:
    des moyens (60, 57) pour générer un signal de brouillage de fréquence variable;
    des moyens (53) pour inclure ledit signal de fréquence variable dans les signaux émis; et
    des moyens (62, 53) pour inclure dans les signaux émis une information représentant la fréquence variable du signal de brouillage; et le récepteur comporte: d e s moyens (20) réagissant à ladite information reçue au niveau du récepteur pour déterminer la fréquence du signal de brouillage; et
    des moyens (21, 25, 26, 30) réagissant auxdits moyens de détermination pour supprimer ledit signal de fréquence variable dans lesdits signaux émis reçus au niveau dudit récepteur.
  2. Système tel que dans la revendication 1, dans lequel la télécommunication transmise est un programme vidéo et le signal de brouillage comporte un signal de brouillage dans la bande de base caractérisé par une fréquence variable dans le temps, et le récepteur comporte: des moyens (13, 17, 18, 20) pour recevoir le programme vidéo brouillé et l'information représentant le signal brouillé; un filtre coupe-bande (30); des moyens de changement de fréquence (26) ayant une première entrée à laquelle est connecté le programme vidéo ayant le signal de brouillage de fréquence variable, une seconde entrée et une sortie connectée audit filtre coupe-bande (30); et des moyens (21, 25) réagissant à l'information provenant de l'émetteur pour fournir à la dite seconde entrée desdits moyens de changement de fréquence (26) un signal de fréquence variable dans le temps approprié pour faire passer la fréquence variable du signal de brouillage à celle du filtre coupe-bande (30).
  3. Système tel que dans la revendication 2, dans lequel ledit récepteur comporte en outre des seconds moyens de changement de fréquence (37) pour faire varier la fréquence de sortie du signal qui a traversé ledit filtre coupe-bande (30).
  4. Système tel que dans la revendication 2 ou 3, dans lequel ledit filtre coupe-bande (30) est à fréquence fixe.
  5. Système tel que dans l'une quelconque des revendications 2 à 4, dans lequel lesdits moyens de fourniture de signaux (21, 25) comportent des moyens de synthèse de fréquence par sauts de fréquences (25).
  6. Système tel que dans la revendication 5, dans lequel ledit filtre coupe-bande (30) a une fréquence de coupure z, le signal de brouillage a une fréquence j', et lesdits moyens de synthèse de fréquence par sauts de fréquences (25) ont une fréquence de sortie z+j', où z et j' sont des nombres positifs indépendants.
  7. Système tel que dans la revendication 5 ou 6, dans lequel lesdits moyens (60, 57, 53) pour inclure un signal de brouillage comprennent en outre des moyens de modulation (62) pour transmettre la fréquence instantanée dudit signal de brouillage et ledit récepteur comporte en outre des moyens de démodulation (20, 21) réagissant à la fréquence du signal de brouillage fourni par lesdits moyens de modulation (62) pour piloter la fréquence desdits moyens de synthèse de fréquence (25).
  8. Système tel que dans l'une quelconque des revendications 2 à 7, dans lequel ledit récepteur comporte en outre un premier filtre passe-bande (18) ayant une capacité en fréquences suffisante pour transmettre ledit programme vidéo, ledit filtre passe-bande (18) étant connecté à ladite première entrée desdits moyens de changement de fréquence (26).
  9. Système tel que dans la revendication 3 ou l'une quelconque des revendications 4 à 8 lorsqu'elles dépendent de la revendication 3, dans lequel lesdits seconds moyens de changement de fréquence (37) ont une entrée connectée audit filtre coupe-bande (30) et une sortie connectée à un second filtre passe-bande (42), ledit second filtre passe-bande (42) ayant une capacité en fréquences suffisante pour transmettre ledit programme vidéo.
  10. Système tel que dans l'une quelconque des revendications 2 à 9, dans lequel ledit récepteur comporte en outre des moyens de détection de demande initiée par le spectateur (53) pour valider sélectivement le fonctionnement desdits moyens de changement de fréquence (26).
  11. Système tel que dans l'une quelconque des revendications précédentes, dans lequel lesdits moyens (60, 57, 53) pour inclure un signal de brouillage fournissent une pluralité de programmes vidéo ayant un signal de brouillage de fréquence variable dans l'un desdits programmes variable dans le temps.
  12. Récepteur destiné à être utilisé avec un système de télécommunication selon l'une quelconque des revendications précédentes, le récepteur comportant
    des moyens (20) réagissant à l'information reçue au niveau du récepteur, représentant la fréquence d'un signal de brouillage de fréquence variable inclus dans un signal reçu, pour déterminer la fréquence du signal de brouillage; et
    des moyens (21, 25, 26, 30) réagissant auxdits moyens de détermination pour supprimer ledit signal de brouillage de fréquence variable dans lesdits signaux émis reçus au niveau dudit récepteur.
  13. Émetteur destiné à être utilisé dans un système de télécommunication selon l'une quelconque des revendications 1 à 11, l'émetteur comportant:
    des moyens (60, 57) pour générer un signal de brouillage de fréquence variable;
    des moyens (53) pour inclure ledit signal de brouillage de fréquence variable dans les signaux émis; et
    des moyens (62, 53) pour inclure dans les signaux émis une information représentant la fréquence variable du signal de brouillage.
EP88312409A 1987-12-30 1988-12-29 Système de distribution de transmissions Expired - Lifetime EP0323258B1 (fr)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
US139459 1980-04-11
US07/139,459 US4841569A (en) 1987-12-30 1987-12-30 Secure video distribution system

Publications (3)

Publication Number Publication Date
EP0323258A2 EP0323258A2 (fr) 1989-07-05
EP0323258A3 EP0323258A3 (en) 1990-11-14
EP0323258B1 true EP0323258B1 (fr) 1996-03-20

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EP88312409A Expired - Lifetime EP0323258B1 (fr) 1987-12-30 1988-12-29 Système de distribution de transmissions

Country Status (5)

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US (1) US4841569A (fr)
EP (1) EP0323258B1 (fr)
AT (1) ATE135870T1 (fr)
DE (1) DE3855129T2 (fr)
IE (1) IE72502B1 (fr)

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Also Published As

Publication number Publication date
DE3855129D1 (de) 1996-04-25
EP0323258A2 (fr) 1989-07-05
ATE135870T1 (de) 1996-04-15
DE3855129T2 (de) 1996-11-21
IE883881L (en) 1989-06-30
EP0323258A3 (en) 1990-11-14
US4841569A (en) 1989-06-20
IE72502B1 (en) 1997-04-23

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